1. Field of the Invention
This invention relates to a process for detecting rotating stall in a turbojet engine having two revolving spools including a high pressure spool and a low pressure spool, wherein the rotation speed of each of the spools is measured. The invention also relates to a device for the detection of rotating stall.
2. Description of the Prior Art
The gas turbine engine shown in FIG. 1 is one illustration of the various types of motors for which the present invention may be employed.
The gas turbine engine illustrated in FIG. 1 is an axial flow by-pass turbine engine including a motor housing (1) in which are mounted, in conventional rotary fashion, a low pressure compressor (2) and its driving turbine (3), as well as a high pressure compressor (4) and its driving turbine (5). A combustion device (6) burns the fuel which it receives from a command (not shown), by releasing gases that propel the turbines (3, 5), while these gases are later expelled through a nozzle so as to produce thrust.
Rotating stall is a phenomenon which affects all turbojet engines under various operating conditions. Although its causes are not well-known, the effects on two-spool engines are almost always the following:
a rapid drop in the exhaust pressure of the compressor (2, 4), followed by an increase in this pressure which is less than the normal rate of increase; PA1 a sudden increase of the temperature (T) of the gas flow at the inlet of the turbines (5, 3), which sometimes manifests itself as a break in the slope of the curve of this temperature as a function of time, and a stabilization of this temperature at levels higher than the normal recommended level; PA1 an increase in the rate of rotation (N.sub.HP) of the high pressure spool (4a, 5) which is less than the normal rate of increase; PA1 an instantaneous stabilization of the rate of rotation (N.sub.BP) of the low pressure spool (2a, 3), followed by a slight increase in this N.sub.BP rate; PA1 sometimes, there are rumbling sounds and an operation reversal called "surge" of the compressor (2, 4).
At the end of a time interval of several seconds, these parameters (T, N.sub.NP, N.sub.BP) stabilize at values that are different from those corresponding to normal stabilization, but, under certain conditions, serious accidents can occur suddenly, such as extinction of the combustion device (6), breakage of blades, etc.
It is therefore important for the pilot or other user to be quickly warned of the appearance of rotating stall or of the imminence of its occurrence so as to be able to take the necessary preventive measures in time.